Christmas tree



FIG. 1 is a front, top and right side perspective view of a Christmas tree showing my new design;

FIG. 2 is a left side elevational view;

FIG. 3 is a top plan view;

FIG. 4 is a rear elevational view;

FIG. 5 is a bottom plan view. 

The ornamental design for a Christmas tree, as shown and described. 